This application is based on and incorporates herein by reference Japanese Patent Applications No. 2000-353179, No. 2001-90786, No. 2001-90795 and No. 2001-276896 filed on Nov. 20, 2000, Mar. 27, 2001, Mar. 27, 2001 and Sep. 12, 2001, respectively.
The invention relates to a flying capacitor type battery voltage detection apparatus.
A battery pack for supplying a high voltage as high as several hundred volts is comprised of many cells (secondary cells or fuel cells) connected in series. This pack is used usually for, for example, a hybrid vehicle, electric vehicle, or fuel battery block electric vehicle in order to reduce the wiring resistance loss and to reduce the size of switching elements.
A high voltage battery pack is provided with a voltage detection apparatus that detects the voltage of each cell for capacity calculation and protection of each cell. A battery block comprising a desired number of cells connected in series is regarded as a cell. Thus the term xe2x80x9ccellxe2x80x9d in this description means a cell comprising a plurality of battery blocks connected in series with each other.
U.S. Pat. No. 6,362,627 (JP-A-11-248755) proposes a battery pack voltage detection apparatus that uses a flying capacitor and multiplexer circuit. This apparatus is referred to as a flying capacitor type battery voltage detection apparatus as an exemplary battery pack voltage detection apparatus.
The flying capacitor type battery voltage detection apparatus detects the voltage difference of the flying capacitor, namely stored voltage, by means of a voltage detection circuit through a process in which the voltage of each cell is applied to a flying capacitor successively through a pair of analog switches of a multiplexer. The cell voltage is sample-held under shutdown condition of both analog switches. Both ends of the flying capacitor is connected conductively to the voltage detection circuit through respective capacitor potential output analog switches.
However, it is preferable for the flying capacitor type battery voltage detection apparatus to be provided with a current limitation resistor having a large resistance value connected in series to each analog switch to prevent the heavy current flow from the battery pack due to short-circuit failure and insulation failure (ground fault failure) of the analog switch of the multiplexer.
However, if a current limitation resistor is provided, it takes a long time that the terminal voltage of a capacitor, namely flying capacitor, reaches the cell voltage. The time required to measure all the cell voltage increases. The increased cell voltage measurement time causes fluctuation of the operation condition in the duration of measurement, particularly fluctuation of current, voltage, temperature, and SOC. This resultantly causes a serious error of the battery pack performance calculated based on the measured cell voltage and current.
This problem can be solved by providing a plurality of capacitors, by increasing the number of analog switches, and by reducing the number of input of each analog switch. However, the circuit structure becomes complicated.
It is therefore an object of the present invention to provide a flying capacitor type battery pack voltage detection apparatus, which has less measurement error and less complication.
According to the present invention, battery cell voltages of a battery pack are read in parallel to capacitors by the use of analog switches. The stored voltages of the capacitors are A/D-converted sequentially through the analog switches. Thereby, each cell voltage is measured with suppression of measurement error by the use of the simple flying capacitor type circuit structure while the circuit safety is secured by providing the current limitation resistor between each cell and the analog switch. A common noise reduction circuit having a pair of capacitors is provided.